JP6190839B2 - Ink composition for ink jet recording and ink jet recording apparatus - Google Patents

Description

  Embodiments described herein relate generally to an ink composition for inkjet recording.

  The ink jet recording method is a method of performing printing by causing ink droplets to fly and adhere to a recording medium. This method is characterized in that a high-resolution and high-quality image can be printed at high speed. The ink jet recording method is employed in printers for plain paper printing used in offices and industrial printers such as label printers.

  In recent years, as ink-jet inks used in industrial printers, inks that use pigment-based colorants instead of those that use dye-based colorants are increasing. This is because an ink using a pigment is superior in water resistance and light resistance as compared with an ink using a dye.

JP-A-11-199811 JP 2003-345080 A JP 2001-081369 A

  The problem to be solved by the present invention is that the ink composition containing a pigment is excellent in adhesion to a non-permeable recording medium without increasing the labor required for maintenance of the ink jet recording apparatus. It is to be able to form a printing layer.

According to the embodiment, an inkjet recording ink composition is a dispersion medium containing water and grayed recall ether, the glycol ether is a dispersion medium only tripropylene glycol monomethyl ether, a pigment, a hydrophobic An ink composition for ink jet recording, comprising: a core made of an acrylic resin; and core-shell particles comprising a shell made of at least one of an aqueous urethane resin and an acrylic grafted aqueous urethane resin, wherein the trio occupying the ink composition proportion of propylene glycol monomethyl ether is in the range of 0.5 to 10 wt%, the proportion of the core-shell particles occupied in the ink composition Ru near the range of 1 to 30 wt%.
According to the embodiment, the ink jet recording apparatus is an ink jet recording apparatus including an ink cartridge and an ink composition housed in the ink cartridge, wherein the ink composition includes water and glycol ether. A dispersion medium in which the glycol ether is only tripropylene glycol monomethyl ether, a pigment, a core made of a hydrophobic acrylic resin, and a shell made of at least one of an aqueous urethane resin and an acrylic grafted aqueous urethane resin. The ratio of the tripropylene glycol monomethyl ether in the ink composition is in the range of 0.5 to 10% by mass, and the ratio of the core shell particles in the ink composition is 1 It exists in the range thru | or 30 mass%.

1 is a diagram schematically showing an example of an ink jet recording apparatus that can be used for ink jet recording using an ink composition according to an embodiment. FIG.

  Hereinafter, an ink composition for ink jet recording according to an embodiment and a recording method using the ink composition will be described.

<Ink composition for inkjet recording>
The ink composition for inkjet recording according to the embodiment contains a dispersion medium, a pigment, and core-shell particles. The pigment and core-shell particles and the dispersion medium form a suspension or emulsion. This ink composition may further contain an additive such as a pigment dispersant.

This ink composition has a viscosity suitable for ejection from a head nozzle of an ink jet recording apparatus, for example, an ink jet printer. According to an example, the ink composition has a viscosity at 25 ° C. of 20 mPa · s or less.
Below, each component of this ink composition is demonstrated.

[Pigment]
The pigment is dispersed in the dispersion medium.
As the pigment, either an inorganic pigment or an organic pigment may be used.

  Examples of the inorganic pigment include titanium oxide, aluminum pigment, and iron oxide. These inorganic pigments may be used in combination with carbon black produced by a known method such as a contact method, a furnace method, or a thermal method.

  Examples of the organic pigment include azo pigments including, for example, azo lake pigments, insoluble azo pigments, condensed azo pigments, and chelate azo pigments; Polycyclic pigments such as linone pigments and quinophthalone pigments; dye chelates such as basic dye-type chelates and acidic dye-type chelates; nitro pigments; nitroso pigments; or aniline black can be used.

  When obtaining a yellow ink composition, it is preferable to use Pigment Yellow 155 as a pigment.

  Pigment yellow 74 is mainly used as the yellow pigment of the ink composition for ink jet recording. This is considered to be because Pigment Yellow 74 is excellent in color developability and dispersion stability. However, Pigment Yellow 74 has low light resistance. Therefore, the printed matter manufactured using the ink composition containing Pigment Yellow 74 is not suitable for outdoor use.

  Pigment Yellow 155 has sufficient color developability and dispersion stability, and also has excellent light resistance. Therefore, the ink composition containing Pigment Yellow 155 is particularly suitable for the production of printed materials used outdoors.

  As the pigment, only one kind can be used. Or you may use 2 or more types as a pigment. For example, Pigment Yellow 155 may be used as the main pigment, and one or more other pigments may be used as the auxiliary pigment. If an auxiliary pigment is used, the color tone can be adjusted.

  As the pigment, a self-dispersed pigment may be used. The self-dispersing pigment is a pigment that has been subjected to surface treatment so that it can be dispersed in water or the like without a dispersant. Here, the surface treatment is, for example, vacuum plasma treatment, diazo coupling treatment, or oxidation treatment. By this surface treatment, for example, at least one functional group of a carbonyl group, a carboxyl group, a hydroxyl group, and a sulfone group or a salt thereof is bonded to the pigment. For example, the functional group or a molecule containing a functional group is grafted onto the surface of the pigment. Thereby, the affinity of the pigment to water and the like is increased, and the pigment can be dispersed in water and the like without a dispersant.

  When using a self-dispersing pigment, a pigment dispersant described later may be used in combination. As described above, the self-dispersing pigment can be dispersed in a dispersion medium such as water without a dispersant. However, when highly hydrophobic substances or core-shell particles are present in such a dispersion medium, the particle size of the pigment may increase over time, or the pigment may aggregate and settle. . When a self-dispersing pigment and a pigment dispersant are used in combination, even if a highly hydrophobic substance or core-shell particles are present in the dispersion medium, the pigment particle size increases or the pigment aggregates over time. And sedimentation can be suppressed.

  The average particle size of the pigment is, for example, in the range of 30 to 300 nm, and typically in the range of 50 to 200 nm.

  The average particle diameter of the pigment can be measured using a particle size distribution meter using a dynamic light scattering method. An example of the particle size distribution meter is HPPS (Malvern).

  The proportion of the pigment in the ink composition is preferably in the range of 2 to 15% by mass, and more preferably in the range of 3 to 10% by mass. If this ratio is reduced, it becomes difficult to achieve a high image density. When this ratio is increased, the storability of the ink composition is lowered, and inconvenience may be caused with respect to ink ejection.

[Core shell particles]
The core-shell particles are dispersed in the dispersion medium.

  The core-shell particle includes a core and a shell surrounding the core. The core is made of a hydrophobic acrylic resin. The shell is made of at least one of an aqueous urethane resin and an acrylic graft aqueous urethane resin.

  The core-shell particles play a role as a fixing agent. The core-shell particles can form a printing layer having excellent adhesion to the recording medium even when the recording medium is impermeable. Moreover, the core-shell particles improve the scratch resistance of the printed layer.

  The ratio of the core-shell particles in the ink composition is preferably in the range of 1 to 40% by mass, more preferably in the range of 1 to 30% by mass, and in the range of 3 to 20% by mass. It is more preferable.

  The core-shell particles exist, for example, as a dispersed phase of an aqueous resin emulsion in which the continuous phase is water until mixed with the pigment. The ink composition can be obtained, for example, by mixing the aqueous resin emulsion and other components such as a pigment.

[Dispersion medium]
The dispersion medium is an aqueous solution containing water and glycol ether.
The glycol ether used here has a boiling point of 220 ° C. or higher. As such a glycol ether, for example, diethylene glycol monoisobutyl ether, diethylene glycol monobutyl ether, tripropylene glycol monomethyl ether, or triethylene glycol monobutyl ether can be used.

  These glycol ethers are difficult to volatilize because of their high boiling points. Moreover, these glycol ethers are excellent in the re-solubility of the emulsion or suspension. Therefore, when this ink composition is used, drying of the ink composition in the vicinity of the nozzle of the inkjet head can be suppressed. Therefore, labor required for maintenance of the ink jet recording apparatus can be reduced.

  The proportion of the glycol ether in the dispersion medium is preferably in the range of 0.5 to 15% by mass, more preferably in the range of 0.5 to 10% by mass, and still more preferably 0.5 to 5%. It is in the range of mass%. When this ratio is small, the above effect is small. If this ratio is increased, the fixability may be reduced.

(Wetting agent)
The dispersion medium can further include a wetting agent that prevents the ink composition from drying. As the wetting agent, a water-soluble liquid wetting agent such as a polyhydric alcohol, a nitrogen-containing heterocyclic compound, an amine, or a sulfur-containing compound can be used. These liquid wetting agents also have an effect of increasing the dispersion stability of the pigment in the ink composition.

  Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, 1,5-pentanediol, 1,6-hexanediol, glycerin, 1,2,6-hexane. Examples include triol, 1,2,4-butanetriol, 1,2,3-butanetriol, and 3-methyl-1,3,5-pentanetriol.

  Examples of the nitrogen-containing heterocyclic compound include N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethylimidazolidinone, and ε-caprolactam.

  Examples of amines include monoethanolamine, diethanolamine, triethanolamine, monoethylamine, diethylamine, and triethylamine.

  Examples of the sulfur-containing compound include dimethyl sulfoxide, sulfolane, and thiodiethanol.

  Examples of liquid wetting agents other than polyhydric alcohols, nitrogen-containing heterocyclic compounds, amines, and sulfur-containing compounds include propylene carbonate, ethylene carbonate, and γ-butyrolactone.

  Among these humectants, glycerin is less likely to volatilize because of its higher water retention and higher boiling point than other humectants. Therefore, it is preferable to use glycerin as at least part of the wetting agent.

  The concentration of the wetting agent in the ink composition is preferably 1 to 40% by mass, and more preferably 2 to 40% by mass.

  Only one type of wetting agent may be used, or two or more types of wetting agents may be used in combination. In order to further improve the wetting effect, the liquid wetting agent described above and a solid wetting agent such as urea, thiourea, and ethylene urea may be used in combination. The ratio of the solid wetting agent to the entire wetting agent is preferably 30% by mass or less.

(Pigment dispersant)
The dispersion medium can further contain a pigment dispersant (or a discharge stabilizer).
The pigment dispersant is, for example, a polymer dispersant or a surfactant.

  Examples of the polymer dispersant include polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylic acid, acrylic acid-acrylonitrile copolymer, acrylic acid-acrylic acid ester copolymer, styrene-acrylic acid copolymer, and styrene-methacrylic acid copolymer. Examples thereof include a polymer and a styrene-maleic acid copolymer.

  Examples of the surfactant include fatty acid salts, higher alkyl dicarboxylates, higher alcohol sulfates, higher alkyl sulfonates, condensates of higher fatty acids and amino acids, sulfosuccinates, naphthenates, liquid fats, and the like. Examples include anionic surfactants such as oil sulfate esters, alkyl allyl sulfonates, polyoxyethylene alkyl ether carboxylates, polyoxyethylene alkyl ether sulfates, and polyoxyethylene alkyl ether ether phosphates.

  As the surfactant, nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, sorbitan alkyl esters, polyoxyethylene sorbitan alkyl esters, and acetylene glycols may be used. .

  Among these, polyoxyethylene anionic surfactants such as polyoxyethylene alkyl ether carboxylate, polyoxyethylene alkyl ether sulfate, and polyoxyethylene alkyl ether phosphate are preferable. When such a surfactant is used as a pigment dispersant, it is possible to suppress an increase in the particle size of the pigment and the aggregation and sedimentation of the pigment over time. Therefore, very good storage stability can be achieved.

  The amount of the pigment dispersant is preferably in the range of 1 to 50% by mass, more preferably in the range of 5 to 40% by mass with respect to the pigment.

(Other additives)
The dispersion medium can further contain other additives.
For example, the dispersion medium may further contain a surface tension adjusting agent.

  As the surface tension adjusting agent, the above-described nonionic surfactant may be used. Examples of the surface tension adjusting agent include polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, sorbitan alkyl esters, polyoxyethylene sorbitan alkyl esters, and acetylene glycols. Moreover, you may use a silicon-type surfactant or a fluorine-type surfactant as a surface tension regulator.

  The concentration of the surface tension agent in the ink composition is preferably in the range of 0.5 to 3% by mass.

The dispersion medium may further contain a pH adjusting agent or an antiseptic or antifungal agent.
Examples of the pH adjuster include sodium hydroxide, potassium hydroxide, potassium dihydrogen phosphate, and disodium hydrogen phosphate.

  Examples of antiseptic or antifungal agents include sodium benzoate, sodium pentachlorophenol, sodium 2-pyridinethiol-1-oxide, sodium sorbate, sodium hydroacetate, and 1,2-dibenzosothiazoline-3-one Is mentioned.

<Recording method>
For inkjet recording using the ink composition described above, for example, an inkjet recording apparatus shown in FIG. 1 can be used.

  The ink jet recording apparatus shown in FIG. 1 includes a housing provided with a paper discharge tray 118. Inside the housing are cassettes 100 and 101, paper supply rollers 102 and 103, conveyance roller pairs 104 and 105, registration roller pair 106, conveyance belt 107, fan 110, negative pressure chamber 111, conveyance roller pairs 112, 113 and 114, Ink jet heads 115C, 115M, 115Y and 115Bk, ink cartridges 116C, 116M, 116Y and 116Bk, and tubes 117C, 117M, 117Y and 117Bk are installed.

  The cassettes 100 and 101 contain recording media P having different sizes. The paper supply roller 102 or 103 takes out the recording medium P corresponding to the size of the selected recording medium from the cassette 100 or 101 and conveys the recording medium P to the conveying roller pairs 104 and 105 and the registration roller pair 106.

  The conveyor belt 107 is tensioned by a driving roller 108 and two driven rollers 109. Holes are provided in the surface of the conveyor belt 107 at predetermined intervals. A negative pressure chamber 111 connected to the fan 110 is installed inside the conveyance belt 107 in order to cause the recording medium P to be adsorbed to the conveyance belt 107. A pair of conveyance rollers 112, 113, and 114 are installed downstream of the conveyance belt 107 in the conveyance direction. Note that a heater for heating the print layer formed on the recording medium P can be installed in the conveyance path from the conveyance belt 107 to the paper discharge tray 118.

  Above the transport belt 107, four rows of inkjet heads that eject ink onto the recording medium P according to image data are arranged. From upstream, an inkjet head 115C that ejects cyan (C) ink, an inkjet head 115M that ejects magenta (M) ink, an inkjet head 115Y that ejects yellow (Y) ink, and an inkjet head that ejects black (Bk) ink The order is 115 Bk.

  The inkjet heads 115C, 115M, 115Y, and 115Bk have cyan (C) ink cartridges 116C, magenta (M) ink cartridges 116M, yellow (Y) ink cartridges 116Y, and black (Bk) inks that accommodate corresponding inks. A cartridge 116Bk is provided. These cartridges 116C, 116M, 116Y and 116Bk are connected to inkjet heads 115C, 115M, 115Y and 115Bk by tubes 117C, 117M, 117Y and 117Bk, respectively.

  The ink composition accommodated in at least one of the ink cartridges 116C, 116M, 116Y, and 116Bk is the ink composition according to the embodiment. Here, as an example, the ink compositions contained in the ink cartridges 116C, 116M, 116Y, and 116Bk are all ink compositions according to the embodiment.

Next, an image forming operation of the ink jet recording apparatus will be described.
First, an image processing means (not shown) starts image processing for recording, generates an image signal corresponding to the image data, and generates a control signal for controlling operations of various rollers, the negative pressure chamber 111, and the like. To do.

  The paper supply rollers 102 or 103 take out the recording medium P of the selected size one by one from the cassette 100 or 101 under the control of the image processing means, and convey it to the conveyance roller pairs 104 and 105 and the registration roller pair 106. To do. The registration roller pair 106 corrects the skew of the recording medium P and conveys the recording medium P at a predetermined timing.

  The negative pressure chamber 111 sucks air through the hole of the conveyor belt 107. Accordingly, the recording medium P is sequentially conveyed to positions below the ink jet heads 115C, 115M, 115Y, and 115Bk as the conveyance belt 107 moves while being attracted to the conveyance belt 107.

  The inkjet heads 115C, 115M, 115Y, and 115Bk discharge ink in synchronization with the timing at which the recording medium P is conveyed under the control of the image processing unit. As a result, a color image is formed at a desired position on the recording medium P.

  Thereafter, the conveyance roller pairs 112, 113, and 114 discharge the recording medium P on which the image is formed to the discharge tray 118. When a heater is installed in the conveyance path from the conveyance belt 107 to the paper discharge tray 118, the print layer formed on the recording medium P may be heated by the heater. When heating with a heater is performed, particularly when the recording medium P is impermeable, the adhesion of the printing layer to the recording medium P can be improved.

  As described above, in this recording apparatus, the ink compositions contained in the ink cartridges 116C, 116M, 116Y, and 116Bk are all ink compositions according to the embodiment. Therefore, not only when the recording medium P is permeable like paper but also when the recording medium P is impermeable, for example, the recording medium P has a smooth recording surface made of plastic, glass or metal. Even if it has, the printing layer excellent in adhesiveness can be formed. In addition, since all of the ink compositions contained in the ink cartridges 116C, 116M, 116Y, and 116Bk are ink compositions according to the embodiment, in this recording apparatus, in the vicinity of the nozzles of the inkjet heads 115C, 115M, 115Y, and 115Bk. It is difficult to cause drying of the ink composition. Therefore, this recording apparatus has a small maintenance burden.

Specific examples are described below.
<Preparation of pigment dispersion>
25 parts by mass of pigment, 5 parts by mass of surfactant, and 70 parts by mass of pure water were mixed, and this mixed solution was subjected to a dispersion treatment using a bead mill. Here, Pigment Yellow 155 was used as a pigment, and polyoxyethylene alkyl ether was used as a surfactant. Further, zirconia beads were used as a grinding medium for the bead mill.

Thereafter, the beads were removed from the dispersion, and the dispersion was subjected to centrifugation and filtration. A 1 μm membrane filter was used for filtration.
As described above, a yellow pigment dispersion containing 25% by mass of pigment was obtained.

<Preparation of ink composition>
The pigment dispersion and other components were mixed according to the formulations shown in Tables 1 to 3 below. In Tables 1 to 3, the numerical values described in the right column of the column displaying the component represent the content (parts by mass) of the component.

  Here, ACRYT (registered trademark) WEM-202UH manufactured by Taisei Fine Chemical Co., Ltd., which is an aqueous resin emulsion, was used as the core-shell particle source. Further, as a discharge stabilizer, Surfhinol (registered trademark) 465 manufactured by Nissin Chemical Industry Co., Ltd. was used. As a preservative, Proxel (registered trademark) xL-2 manufactured by Lonza was used.

  This mixed solution was stirred for 1 hour using a stirrer, and then filtered through a 1 μm membrane filter. Thereby, an ink composition was obtained.

<Evaluation of maintainability>
Using each of the ink compositions shown in Tables 1 to 3, printing was performed using an inkjet recording apparatus. Here, an inkjet recording apparatus manufactured by Toshiba Tec Corporation was used. After printing, the ink jet head was fixed at a position away from the home position, and was left under a temperature condition of 25 ° C. for 24 hours. Thereafter, printing was performed again, and the ejection stability of the inkjet head was examined. Then, the maintainability was evaluated in light of the discharge stability in accordance with the following criteria. The results are summarized in Tables 1 to 3.

A: Discharge immediately after standing was unstable, but stable discharge was possible immediately without a cleaning operation.
○: Discharge immediately after standing was unstable, but stable discharge became possible by cleaning operation within two times.
Δ: Discharge immediately after standing was unstable, but stable discharge became possible by three or more cleaning operations.
X: Discharge immediately after being left unsettled was unstable, and stable discharge could not be performed even after repeated cleaning operations.

<Evaluation of storage stability>
For each of the ink compositions shown in Tables 1 to 3, the viscosity and surface tension of the ink composition were measured.

  Further, 100 cc of each of the ink compositions shown in Tables 1 to 3 was weighed and placed in a glass sample bottle. The bottle was sealed and stored for 60 days in a high temperature bath set at 50 ° C. Thereafter, the viscosity and surface tension of the ink composition were measured, and the presence or absence of a precipitate was examined.

  And these results were evaluated in light of the following criteria to evaluate the storage stability. The results are summarized in Tables 1 to 3.

○: There was almost no change in physical properties, and there was no precipitation.
Δ: A large physical property change or a large amount of precipitate was not generated, but a slight physical property change was observed or a small amount of precipitate was generated.
X: A large physical property change or a large amount of precipitate was generated.

<Evaluation of adhesion>
First, printing was performed using an ink jet recording apparatus using each of the ink compositions shown in Tables 1 to 3.

  Here, solid printing was performed on a square area having a side of 10 mm on a recording medium using an inkjet recording apparatus manufactured by TOSHIBA TEC equipped with a piezo head. The printed layer thus formed was heated with a dryer for 10 seconds. At this time, the surface temperature of the recording medium was 50 ° C. or less.

Further, as the recording medium, an impermeable recording medium made of the following material was used.
Polyvinyl chloride Polyethylene terephthalate Stainless steel Aluminum Glass

  Next, an adhesive tape was applied to the print layer, and this adhesive tape was rubbed with a finger three times. As the adhesive tape, Scotch (registered trademark) mending tape 810 manufactured by Sumitomo 3F was used. Thereafter, the adhesive tape was peeled off, and the state of the printed layer was visually observed. And this state was evaluated in light of the following criteria, and adhesiveness was evaluated.

○: No pigment was removed from the recording medium.
Δ: A small amount of pigment dropped from the recording medium.
X: A large amount of the pigment was removed from the recording medium.

Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.
The invention described in the original claims is appended below.
[1]
A dispersion medium containing water and a glycol ether having a boiling point of 220 ° C. or higher;
Pigments,
An ink composition for ink-jet recording comprising a core made of a hydrophobic acrylic resin and core-shell particles comprising a shell made of at least one of an aqueous urethane resin and an acrylic grafted aqueous urethane resin.
[2]
The ink composition for ink jet recording according to [1], wherein the ratio of the core-shell particles in the ink composition is in the range of 1 to 30% by mass.
[3]
The ink composition for ink jet recording according to [1] or [2], wherein the proportion of the glycol ether in the ink composition is in the range of 0.5 to 10% by mass.
[4]
The ink composition for ink jet recording according to any one of [1] to [3], wherein the glycol ether is tripropylene glycol monomethyl ether.
[5]
The ink composition for ink jet recording according to any one of [1] to [4], wherein the dispersion medium further contains glycerin.

  DESCRIPTION OF SYMBOLS 100 ... Cassette, 101 ... Cassette, 102 ... Paper feeding roller, 103 ... Paper feeding roller, 104 ... Conveying roller pair, 105 ... Conveying roller pair, 106 ... Registration roller pair, 107 ... Conveying belt, 110 ... Fan, 111 ... Negative Pressure chamber, 112 ... conveying roller pair, 113 ... conveying roller pair, 114 ... conveying roller pair, 115Bk ... inkjet head, 115C ... inkjet head, 115M ... inkjet head, 115Y ... inkjet head, 116Bk ... ink cartridge, 116C ... ink cartridge 116M ... ink cartridge, 116Y ... ink cartridge, 117Bk ... tube, 117C ... tube, 117M ... tube, 117Y ... tube, 118 ... paper discharge tray, P ... recording medium.

Claims (4)

A dispersion medium containing water and grayed recall ether, the glycol ether is a dispersion medium only tripropylene glycol monomethyl ether,
Pigments,
An ink composition for ink jet recording comprising a core made of a hydrophobic acrylic resin and core-shell particles comprising a shell made of at least one of an aqueous urethane resin and an acrylic grafted aqueous urethane resin ,
The proportion of the tripropylene glycol monomethyl ether in the ink composition is in the range of 0.5 to 10% by mass,
The ink composition for ink jet recording, wherein the ratio of the core-shell particles in the ink composition is in the range of 1 to 30% by mass . The ink composition for inkjet recording according to claim 1, wherein the dispersion medium further contains glycerin. An ink cartridge;
  An ink composition contained in the ink cartridge;
An ink jet recording apparatus comprising:
  The ink composition is
  A dispersion medium containing water and glycol ether, wherein the glycol ether is only tripropylene glycol monomethyl ether;
  Pigments,
  Containing core-shell particles comprising a core made of a hydrophobic acrylic resin and a shell made of at least one of an aqueous urethane resin and an acrylic grafted aqueous urethane resin,
  The proportion of the tripropylene glycol monomethyl ether in the ink composition is in the range of 0.5 to 10% by mass,
  An ink jet recording apparatus in which a ratio of the core-shell particles in the ink composition is in a range of 1 to 30% by mass. The inkjet recording apparatus according to claim 3, wherein the dispersion medium further contains glycerin.